Search

Annealing temperatures and applied magnetic fields are two important parameters for the performance modification of magnetic alloys. This article investigated the effect of different annealing temperatures on crystallization condition, magnetic properties and thermal stability of the amorphous magnetic alloy Co36Fe36Si4.8B19.2Nb4 (at%). Results indicate that the annealing temperature can significantly affect the size and content of precipitated nanocrystals in the amorphous alloy, and the precipitation of nanocrystalline phases can result in the distinct change of magnetic properties and Curie temperature. When the annealing was performed at 595 °C for 30 min under an applied transverse external magnetic field of 9550.0 A·m−1, the amorphous alloy shows excellent soft magnetic properties with the saturation magnetization of alloy reaching 110.00 mA·m2·g−1, the residual magnetic induction intensity of 4 × 10−6 T and the coercivity as low as 57.3 A·m−1. Furthermore, the Curie temperature of the field-annealed samples can reach up to 440 °C, approximately 58 °C higher than that of the as-quenched species. [ABSTRACT FROM AUTHOR]

In the present study the magnetic, magneto-optical, morphological and microstructural properties of the amorphous Fe 83 Cu 1 Nb 3 Si 5 B 8 alloy were thoroughly investigated in accordance with various annealing circumstances. The kinetic nanocrystallization temperatures of certain ribbon were determined at the range of 500–515 °C. Furthermore, optimum heat treatment conditions were sought in the air atmosphere (AA), in vacuum (VA) and in vacuum with the presence of longitudinal magnetic field (LFA) at 70 A/m. This study aimed to put forward a quantitative explanation of the advantages of LFA in terms of several factors such as magnetic properties, microstructural evaluation and magneto-optical effects. The present nanocrystalline Fe 83 Cu 1 Nb 3 Si 5 B 8 alloy has allowed the yielding of ultrafine grain structure correlated with the literature results. Accordingly, average grain size of 5.9 nm, saturation induction of 1.84 T and coercivity of 6.4 A·m−1 and saturation magnetostriction as low as 6 ppm were obtained as a result of LFA implementation. However, the sample subjected to VA under the same circumstances showed relatively lower magnetic and microstructural capability, with an average grain size of 9.8 nm, saturation induction of 1.73 T, coercivity of 14.7 A·m−1 and saturation magnetostriction of 14 ppm, in comparison with LFA. To ensure precise average grain size, both XRD data and TEM micrographs were separately considered. Even though saturation magnetostriction could not be completely eliminated, it was significantly minimized from 52 ppm to 35 ppm, 14 ppm and 6 ppm in the samples subjected to AA, VA and LFA, respectively. • Ideal requirements were found in the LFA sample at 510 °C during 1 h. • Mean grain size of LFA sample were found by 7.02 nm (TEM) and 6.27 nm (XRD). • Scherrer was found insufficient once the grain sizes are enlarged (after 20 nm). • The stress domination was completely relieved after LFA implementation. • Fraction of the crystalline phase was measured around 90% for LFA sample. [ABSTRACT FROM AUTHOR]

The roles of applied magnetic field during the current annealing of Co 68.15 Fe 4.35 Si 12.5 B 15 soft magnetic amorphous ribbons are studied. Samples heat treated by Joule heating effect in open air and simultaneously in the present of longitudinal external magnetic field showed asymmetric magnetoimpedance (AMI) behavior. The AMI profile can be related to the exchange bias interaction between the soft magnetic amorphous material and a harder magnetic crystalline phase formed on the surface of the ribbon. This effect stems from thermal effect, the transverse Oe field generated from the annealing current which is thickness dependent and the longitudinal external field. The single peak AMI with the field sensitivity of 101%/Oe for DC annealing current is achieved. Our results could address a simple way to achieve the AMI response toward developing high sensitive magnetic field sensors. [ABSTRACT FROM AUTHOR]

Abstract: The possibilities to improve the performance of certain fluxgate sensor types are still not exhausted. Two types of closed-path sensors – ring core and racetrack – were checked to reveal risky combination of material and construction parameters, and means to optimize the combination were tested. One-step field annealing of Co-based metallic glass was chosen to acquire low-magnetostrictive material with anisotropy required to reduce noise by favoring magnetization rotation. Locally misaligned anisotropy promoted incoherent rotation and handicapped racetrack noise performance. Despite the risk of bending stress aggravated by small – 12mm diameter, the ring cores fared better and reproducibly achieved noise 7pT/√Hz @ 1Hz when thoroughly fixed an annealed in an optimal sheath. As far as we know these are the lowest noise values achieved for this size of fluxgate sensors. [Copyright &y& Elsevier]

Abstract: A ribbon of a Mn-Bi meta-stable phase was fabricated by melt-spinning a Bi-rich Mn-Bi alloy (Mn10Bi90). Employing magnetic field heating to an as-spun sample up to 530K in a magnetic field of 10kOe results in a highly c-axis preferred orientation, showing the remanence magnetization ratio M r/M s ≈1.0 on the demagnetization curve for the heat-treated sample. The magnetic field heating also produces the c-axis preferred orientation in an ex situ annealed sample composed of MnBi particles with a random c-axis orientation. Investigating magnetization change upon changing the heating temperature suggests that MnBi particle rotation at an optimized heating temperature plays an important role in aligning the c-axis along the applied field. [Copyright &y& Elsevier]

Abstract: The effect of both longitudinal and transverse magnetic field applied during the heat treatment on the magnetic properties of HITPERM-type alloys has been investigated. The strongest response to the field annealing is found for the alloys with Fe/Co ratio close to the equiatomic composition . After annealing in a transverse magnetic field, the induced anisotropies up to have been obtained. A heat treatment under presence of longitudinal magnetic field results in squared hysteresis loops characterized by the coercive field values in the range 6–10A/m. These values are superior to those previously reported for HITPERM materials and we show that they remain fairly stable also at elevated temperatures. The differences in the development of induced anisotropy in the series of alloys with varying Fe/Co ratio are discussed in the frame of the magnetic atoms pair ordering theory. [Copyright &y& Elsevier]

Abstract: We report the influence of composition and very high transverse field annealing on the magnetic properties and structure of four FeCo-based amorphous and nanocrystalline alloys. The compositions (Fe50Co50)89Zr7B4 and (Fe65Co35)89Zr7B4 were investigated changing the Fe:Co ratio from 50:50 to 65:35. (Fe50Co50)85Zr2Nb4B8.5 was chosen to investigate Nb substitution for Zr in an FeCo-based alloy. This substitution is shown to increase the magnetostrictive constant, , of the nanocrystalline alloy from 36×10−6 to 54×10−6. The composition (Fe65Co35)84Cr5Zr7B4 was studied to investigate the influence of Cr on intergranular coupling across the amorphous matrix. Samples of each composition were annealed in the amorphous state at 300°C and in the nanocrystalline state at 600°C. Field annealing was performed in 17T transverse field in an inert atmosphere. Frequency-dependent magnetic properties were measured with an automatic recording hysteresisgraph. Static magnetic properties were measured with a vibrating sample magnetometer. The mass-specific power loss of the alloys decreased with field annealing in both the nanocrystalline and amorphous states for some frequency and induction combinations. Furthermore, the hysteresis loops are sheared after field annealing, indicating a transverse magnetic anisotropy. The nanocrystalline (Fe50Co50)85Zr2Nb4B8.5 composition has a lower relative permeability than the other compositions. [Copyright &y& Elsevier]

A self-biasing magnetostrictive element for a magnetomechanical Electronic Article Surveillance (EAS) marker is fabricated by annealing a ribbon of ferromagnetic amorphous material (Co47.4Fe31.6Si2Bi19) in a presence of magnetic field applied in a transverse direction relative to the ribbon’s longitudinal axis, and then annealing in a presence of magnetic field applied in the direction of the longitudinal axis. The two-step annealed ribbon exhibits remanent magnetization along the longitudinal axis and has plural magnetic domains situated along the longitudinal axis. The magnetic orientation of each domain is canted by ± 03B8; < 90° from the ribbon axis with the direction of canting alternating from domain to domain. To obtain such a canted anisotropy, theoretical background for the calculation of the field strength (H) and canted angle (θ) is described. [ABSTRACT FROM AUTHOR]

• Investigation of the memory effect underlying the establishment of induced anisotropy. • Experiment method to boost the field applied to the treated cores during annealing. • Polarization during the annealing have been investigated through simulation process. We study the relation between the induced anisotropy obtained on nanocrystalline Fe 73.0 Cu 1.1 Nb 3.1 Si 15.7 B 7.1 toroidal cores crystallized under transverse field at 570 °C, and the polarization J c of nanograins. To do this, an original disposition is used, mixing treated cores with cores made of electrotechnical SiFe alloy, featuring same geometry, using the interfacial magnetic charges to increase the field in treated cores. The field supplied by the coil being μ 0 H a = 33 m T , playing on the proportion between treated and SiFe cores, effective field ranging between 33 m T and 230 m T were obtained inside treated cores. As a result, the induced anisotropy at the scale of the alloys at the end of crystallization range from K u = 12 J / m 3 to K u = 20 J / m 3. To simulate the evolution of J c during the crystallization process, the configuration of treated and SiFe cores in the sample holder was implemented in Altair FluxT FEM simulation environment with the dedicated polarization laws. Dealing with treated cores, the law J cor (H) at the scale of the core reflects the law J c H featured by nanograins during the crystallization process. J c H was modelized as a function of the crystallized fraction f c. The relation between the simulated J c and the experimental final values of K u / f c (i.e. the anisotropy in nanograins) was then studied. This was done considering the polarization 〈 J c 〉 averaged on the entire crystallization process, wondering about a possible memory effect. [ABSTRACT FROM AUTHOR]

Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe44.5Co44.5ZrγB4 were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600 °C for 1 h, then, field annealed at 17 tesla (T) at 4800 C for 1 h. Another set was crystallized in a 17-T field at 480 °C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient λs is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized-than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy However, reannealing the samples in the absence of a magnetic field at 480 °C does not completely remove the induced anisotropy. [ABSTRACT FROM AUTHOR]

The effect of field annealing on the magnetic tunnel junctions (MTJs) with an artificial antiferromagnetic layer is investigated. Samples, which were grown under the same condition, are annealed with low (200-Oe) and high (1-kOe) magnetic fields. The rotation of the pinned direction is observed for the sample annealed at high magnetic field without decrease of tunneling magnetoresistance by varying the applied field direction. This result provides a method to adjust the pinned direction of the MTJ, which may be critical in switching a magnetic RAM (MRAM) cell. [ABSTRACT FROM AUTHOR]

The magnetic anisotropy field distribution is discussed for Co‐based amorphous ribbon annealed under different field conditions leading to different induced anisotropies: longitudinal field (LF) and transversal field (TF) annealing. In order to understand the relation between the field annealing‐induced anisotropy and the performance of meander‐core orthogonal fluxgate sensor, field‐annealed ribbons with different in‐plane anisotropies as cores of orthogonal fluxgate sensors are employed and both noise and sensitivity in fundamental mode are measured. Experimental results indicate that LF annealing‐induced anisotropy with easy axis perpendicular to the direction of excitation field can effectively improve the sensor sensitivity. On the other hand, TF annealing‐induced anisotropy with easy axis parallel to excitation field results in lower sensitivity, but the noise is also lower. The results obtained are useful for developing the high‐performance orthogonal fluxgate sensors based on amorphous ribbon cores. This paper studies the magnetic anisotropy field distribution for Co‐based amorphous ribbon annealed under longitudinal field (LF) and transverse field (TF). Furthermore, the influences of field annealing‐induced magnetic anisotropy on the performance of meander‐core orthogonal fluxgate sensors are investigated. It is an interesting work which is important in the performance improvement of magnetic sensors based on amorphous materials. [ABSTRACT FROM AUTHOR]

Abstract: Fe50Co50 thin films with thickness of 30 and 4nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350°C for times between 20 and 120min, under a static magnetic field of 100Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4nm display lower coercive fields with respect to the 30nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30nm thick films. [Copyright &y& Elsevier]